Device architecture and method for precision enhancement of vertical semiconductor devices

ABSTRACT

Improvement of key electrical specifications of vertical semiconductor devices, usually found in the class of devices known as discrete semiconductors, has a direct impact on the performance achievement and power efficiency of the systems in which these devices are used. Imprecise vertical device specifications cause system builders to either screen incoming devices for their required specification targets or to design their system with lower performance or lower efficiency than desired. Disclosed is an architecture and method for achieving a desired target specification for a vertical semiconductor device. Precise trimming of threshold voltage improves targeting of both on-resistance and switching time. Precise trimming of gate resistance also improves targeting of switching time. Precise trimming of a device&#39;s effective width improves targeting of both on-resistance and current-carrying capability. Device parametrics are trimmed to improve a single device, or a parametric specification is targeted to match specifications on two or more devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority benefit from U.S. ProvisionalApplication No. 61/729,720 filed Nov. 26, 2012. The patent applicationidentified above is incorporated here by reference in its entirety toprovide continuity of disclosure.

TECHNICAL FIELD OF THE INVENTION

This invention relates generally to the methods and techniques forimproving the specifications of vertical semiconductor devices. Inparticular, this invention details novel methods for improving variousparametric specifications of vertical semiconductor devices utilizingdevice trimming.

BACKGROUND OF THE INVENTION

Semiconductor manufacturing processes must balance competing goals ofcost, yield, and performance. While market demands drive manufacturersto reduce costs, improved system performance drives ever-tightercomponent tolerances. In many applications, the system performancerequirements exceed what can be attained in a cost effectivemanufacturing process.

Similar issues exist in the manufacture of power supply components, forexample, the variations in parametric distributions of discrete devicessuch as VDMOS, IGBTs, and vertical power diodes limit efficiency andswitching speed in system designs.

Two primary design parameters of interest to power supply designers arethe threshold voltage (V_(t)) and gate resistance of the switching VDMOSdevice. Variations in V_(t) and gate resistance determine system timingconstraints that propagate into overall power supply efficiency ratingsfor the circuit utilizing the device. Tighter and more accurate controlof V_(t) and gate resistance distributions provides many advantages. Forexample, some of these advantages include closer system timing,reduction in guard bands, lower switching losses, and increasedefficiency. There are several device parameters of this nature where theabsolute value of the parameter is not as important as the width of thevariation observed for the parameter. Tighter controls of thesedistributions would allow the designer the flexibility to make tradeoffsin the system design, improving a particular performance characteristicas needed for a particular application.

Various techniques have been employed over the years to tightenparametric distributions from a cost effective manufacturing process,but none have been completely satisfactory.

One solution of the prior art has been to concentrate on low costprocessing, test the resulting components, and sort the manufactureddevices into various parametric distribution categories and to chooseonly those which are in an acceptable range. However, this approachraises cost because large numbers of parts from the overall populationoutside the distribution range must be discarded.

Another approach of the prior art has been to modify the design of thecomponents slightly to allow trimming with a laser or otherpost-fabrication techniques to shift large numbers of the parts into adesired parametric range. However, this method has not been successfullyapplied to vertical semiconductor devices. The reason that trimmingtechniques are difficult to apply to vertical semiconductor devices isbecause the internal units making up the vertical device all have acommon connection on the bottom side of the wafer. For example, thebottom side of the wafer for a VDMOS is the common drain terminal forall internal units making up the device. The bottom side of the waferfor an IGBT is the common collector terminal for all internal unitsmaking up the device. In order to implement trimming on devices likethese with common terminals, novel techniques such as those described inthe present invention can be utilized.

SUMMARY OF THE DISCLOSURE

“Vertical” semiconductor devices are semiconductor devices where theprimary direction of current flow is vertical. Power discretesemiconductor devices are often built as vertical semiconductor devices.

According to a preferred embodiment, a method is provided for targetingvia laser trimming a specific threshold voltage of a VDMOS, IGBT, orvertical gated-diode using at least two parallel device groups, witheach group having a different threshold voltage, with these differentthreshold voltages bracketing the target threshold voltage. The samemethod may be used to match the threshold voltage of two or more VDMOSs,IGBTs, or vertical gated-diodes on the same or on separate die.

According to another preferred embodiment, a method is provided fortargeting via laser trimming a specific on-resistance orcurrent-carrying capability of a VDMOS, IGBT, or vertical diode usingmultiple parallel device segments. The same method may be used to matchthe on-resistance or current-carrying capability of two or more VDMOSs,IGBTs, or vertical diodes on the same or on separate die.

According to another preferred embodiment, a method is provided fortargeting via laser trimming a specific switching time of a VDMOS orIGBT using multiple parallel gate resistors. The same method may be usedto match the switching time of two or more VDMOSs or IGBTs on the sameor on separate die.

According to another preferred embodiment, a method is provided fortargeting via laser trimming a specific switching time of a VDMOS orIGBT using both multiple parallel device segments with at least twodifferent threshold voltages and multiple parallel gate resistors. Thesame method may be used to match the switching time of two or moreVDMOSs or IGBTs on the same or separate die.

According to another preferred embodiment, a method is provided fortargeting via laser trimming a specific gate resistance of a VDMOS orIGBT using multiple parallel gate resistors. The same method may be usedto match the gate resistance of two or more VDMOSs or IGBTs on the sameor separate die.

According to another preferred embodiment, a method is provided fortargeting via laser trimming a specific breakdown voltage of a verticaldiode using multiple parallel device elements with at least twodifferent breakdown voltages which bracket the target breakdown voltage.The same method may be used to match the breakdown voltage of two ormore vertical diodes on the same or on separate die.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a primary element group having a non-trimmablesection with a first threshold voltage, for use in a composite VDMOSdevice.

FIG. 1B illustrates a combination of two element groups, having trimsections with two different threshold voltages.

FIG. 1C illustrates the nth element group having multiple trim sectionsand an nth threshold voltage, for use in a trimmable composite VDMOSdevice.

FIG. 1D illustrates an example configuration of an element group for usewithin a trimmable composite VDMOS device having multiple trim sections.

FIG. 2 illustrates a procedure for trimming an element group withmultiple trim sections from an untrimmed composite threshold voltage toachieve a target threshold voltage.

FIG. 3A illustrates a trimmable composite VDMOS device having a primarydevice interconnected with an element group of multiple trim sections.

FIG. 3B illustrates a device layout for a trimmable composite VDMOSdevice.

FIG. 4 illustrates a procedure for trimming a trimmable composite VDMOSdevice having multiple trim sections to achieve a target on-resistance.

FIG. 5A illustrates a composite VDMOS device having a trimmable gateresistor with trimmable sections connected in parallel and with eachtrimmable section having a resistor in series with a trim fuse.

FIG. 5B illustrates an example configuration of a trimmable gateresistor.

FIG. 6 illustrates a procedure for trimming the switching time of acomposite VDMOS device having a trimmable gate resistor where theswitching time is trimmed to achieve a target switching time.

FIG. 7 illustrates a composite VDMOS device having a trimmable gateresistor connected in series with a set of trimmable composite deviceswhere the composite VDMOS device has a trimmable switching time which isachieved by first trimming the threshold voltage and subsequentlytrimming the gate resistance.

FIG. 8 illustrates a procedure for trimming the switching time and thethreshold voltage of a composite VDMOS device having a trimmable gateresistor and a set of trimmable composite devices.

FIG. 9A illustrates a composite VDMOS device having trimmable gateresistor with reduced parasitic capacitance including trimmable sectionsconnected in parallel and with each trimmable section having a resistorin series with a pair of trim fuses.

FIG. 9B illustrates an example configuration of a trimmable gateresistor with reduced parasitic capacitance.

FIG. 10 illustrates a procedure for trimming the gate resistance of acomposite VDMOS device having a trimmable gate resistor from anuntrimmed composite gate resistance to achieve a target gate resistance.

FIG. 11A illustrates a primary element group having a singlenon-trimmable element and a first breakdown voltage for use in acomposite diode device.

FIG. 11B illustrates an element group for use in a trimmable compositediode device having at least two trim elements and a selectablebreakdown voltage.

FIG. 11C illustrates an nth element group having one or more trimelements and an nth breakdown voltage, for use in a trimmable compositediode device.

FIG. 11D illustrates an example configuration of an element group havingmultiple trim elements and a configured strength of breakdown voltageV_(n), for use in a trimmable composite diode device.

FIG. 12 illustrates a procedure for trimming the breakdown voltage of atrimmable composite diode device having multiple trim elements withmonotonically increasing breakdown voltages.

DETAILED DESCRIPTION

While the making and using of various embodiments of the presentdisclosure are discussed in detail below, it should be appreciated thatthe present disclosure provides many applicable inventive concepts thatcan be embodied in a wide variety of specific contexts. The specificembodiments discussed herein are merely illustrative of specific ways tomake and use what is disclosed and do not limit its scope.

“Threshold voltage,” in a MOSFET transistor device having a gateterminal, source terminal and a drain terminal, is understood to meanthe value of the gate-source voltage V_(GS) when the conducting channelof the device just begins to connect the source terminal and the drainterminal of the device, allowing significant current to flow between thesource and drain terminals.

“On-resistance” is commonly understood to be the resistance of asemiconductor device when it is biased in the on-state by applyingcertain voltages and/or currents to its terminals. For a VDMOS device,for example, on-resistance is often defined as drain current (I_(d))divided by drain-source voltage (V_(ds)) when V_(ds) is set to 0.1V andthe gate-source voltage (V_(gs)) is set to 10V.

“Switching time” refers to the time that it takes for a device to switchfrom its “off” state to its “on” state or from its “on” state to its“off” state. Switching time is measured by computing the time requiredfor the off state to rise from 10% to 90% of its average on state valueof either voltage or current, thus turning the device on, or the timerequired for the on state to fall from 90% to 10% of its average onstate value of either voltage or current, thus turning the device off.“Effective width” of a semiconductor device is the width of conductingregion of the device. Larger effective width allows the device to carrya larger amount of current, and smaller effective width restricts thedevice to carry a smaller amount of current. A device having a largereffective width will also have a smaller on-resistance than a devicehaving a smaller effective width.

The Vertical-Diffused MOSFET or Vertical-Drift MOSFET (VDMOS) is aMOSFET transistor in which the flow of current is vertical, usually fromtop to bottom. In older generations of processing, the channel region ofthis device type, of opposite doping polarity to the source and drain ofthe device, was created by a high temperature diffusion step, hence the“Diffused” in the name. The “Diffused” name is sometimes replaced by theterm “Drift” today, as most modern devices employ some type of Driftregion to support high voltages.

A vertical diode is a diode in which the anode is located on one surfaceof the device and the cathode is located on the opposite surface of thedevice, so that the primary direction of current flow is perpendicularto these surfaces.

The breakdown voltage of a vertical diode is commonly defined as thevoltage at which the off state device begins to electrically break downand pass a specified level of current.

The Insulated-Gate Bipolar Transistor (or IGBT) is a vertical currentflow Bipolar transistor which employs an insulated gate terminal (verysimilar to the gate terminal of a MOSFET) to turn the device on andinitiate current flow, and for turning the device off and stoppingcurrent.

Referring to FIG. 1A, a device element 100 includes a VDMOS device 104having a gate electrode 102, a source electrode 108 and a drainelectrode 106. VDMOS device 104 has a threshold voltage V_(t1). In use,a voltage V_(DS) is applied between the drain electrode and the sourceelectrode and a voltage V_(GS) is applied between the gate electrode andthe source electrode. Device element 100 forms a basic device used in atrim section of a device element group with multiple trim sections.

Referring to FIG. 1B, an element group 110 includes two interconnectedVDMOS device trim sections, trim section 111 and trim section 112.Element group 110 has a gate terminal 119, a drain terminal 122 and asource terminal 123. In use, a voltage V_(DS) is applied between thedrain terminal and the source terminal and a voltage V_(GS) is appliedbetween the gate terminal and the source terminal.

Trim section 111 includes device 113, with its drain electrode connectedto drain terminal 122 and its source electrode connected to sourceterminal 123. The gate electrode of device 113 is connected to gateterminal 119 through isolation fuse 120. The gate electrode of device113 is further connected to source terminal 123 through pull-downresistor 115 in series with activation fuse 117. Device 113 exhibits athreshold voltage V_(t2).

Trim section 112 includes device 114, with its drain electrode connectedto drain terminal 122 and its source electrode connected to sourceterminal 123. The gate electrode of device 114 is connected to gateterminal 119 through isolation fuse 121 and isolation fuse 120 which areconnected in series. The gate electrode of device 114 is furtherconnected to source terminal 123 through pull-down resistor 116 inseries with activation fuse 118. Device 114 exhibits a threshold voltageV_(t3). Element group 110 has a selectable threshold voltage of V_(t2)or V_(t3).

Referring to FIG. 1C, an example composite VDMOS device 130 consists ofn interconnected VDMOS device sections including non-trimmable section131 and trim sections 132 and 133. There are (n−3) trim sectionsinterconnected between trim section 132 and trim section 133. Compositedevice 130 has a gate terminal 143, a drain terminal 147 and a sourceterminal 148. A set of n isolation fuses including isolation fuses 145and 146 are connected in series to gate terminal 143. In use, a voltageV_(DS) is applied between the drain terminal and the source terminal anda voltage V_(GS) is applied between the gate terminal and the sourceterminal.

Non-Trimmable section 131 includes device 134, with its drain electrodeconnected to drain terminal 147 and its source electrode connected tosource terminal 148. The gate electrode of device 134 is connected togate terminal 143. Device 134 exhibits threshold voltage V_(t1).

Trim section 132 includes device 135, with its drain electrode connectedto drain terminal 147 and its source electrode connected to sourceterminal 148. The gate electrode of device 135 is connected to gateterminal 143 through isolation fuse 145. The gate electrode of device135 is further connected to source terminal 148 through pull-downresistor 138 in series with activation fuse 141. Alternatively, theactivation fuse 141 can be placed between the pull-down resistor 138 andthe gate of device 135 in order to reduce any parasitic resistanceassociated with the pull-down resistor. Device 135 exhibits thresholdvoltage V_(t2).

Trim section 133 includes device 136, with its drain electrode connectedto drain terminal 147 and its source electrode connected to sourceterminal 148. The gate electrode of device 136 is connected to gateterminal 143 through isolation fuse 145, isolation fuse 146 and allintermediate isolation fuses connected in series between isolation fuse146 and isolation fuse 145. The gate electrode of device 136 is furtherconnected to source terminal 148 through pull-down resistor 139 inseries with activation fuse 142. Device 136 exhibits threshold voltageV_(tn).

There are (n−3) intermediate trim sections between trim section 132 and133 in composite device 130 interconnected similarly as trim section 132and 133 to gate terminal 143, drain terminal 147 and source terminal148. One or more trim sections may have the same threshold voltage valuefor trimming purposes. Example composite device 130 has selectablethreshold voltage in range of threshold voltages between V_(tn) andV_(t1), where, V_(tn)<V_(t2)<V_(t1).

When an activation fuse is connected, for example as in activation fuse142, a shunt is formed through pull-down resistor 139 and activationfuse 142 where current flows from the gate terminal to the sourceterminal. Because of the shunt, insufficient current flows from the gateterminal to the source terminal through device 136 in order to allowdevice 136 to conduct.

A trim section is “activated” when its corresponding activation fuse is“blown”. A trim section is electrically “isolated” from the elementgroup when at least one isolation fuse between the trim section and thegate terminal 143 is “blown.” In the embodiment of FIG. 1C, no trimsections are “isolated” and no trim sections are “activated.” In anumber of additional embodiments, there are a number of differentconfigurations of composite device 130 which are selectable by blowingisolation and activation fuses.

Referring to FIG. 1D, a further example of isolation and activation oftrim sections is provided. In FIG. 1D, element group 150 consists of ninterconnected VDMOS device sections including non-trimmable section 151and trim sections 152, 153 and 154. Each trim section includes a VDMOSdevice with a gate electrode, a source electrode and a drain electrode.There are (n−4) trim sections 155 between trim section 153 and 154.Element group 150 has a gate terminal 156, a drain terminal 157 and asource terminal 158. In use, a voltage V_(DS) is applied between thedrain terminal and the source terminal and a voltage V_(GS) is appliedbetween the gate terminal and the source terminal.

A set of n isolation fuses including isolation fuses 172, 173 and 174are connected in series to gate terminal 156. Isolation fuses 173 and174 are blown, thereby disconnecting gate terminal 156 from trim section153 and from trim section 154. Blowing isolation fuse 173 also resultsin a cascading isolation of trim sections 155 which are alsodisconnected from the gate terminal. Trim sections 153, 154 and 155 aretherefore electrically isolated from the gate terminal and do not drawany current as a result of V_(GS) or V_(DS) and do not contribute to theoperation of element group 150.

A set of n activation fuses include activation fuses 162, 163 and 164connecting the gate electrodes in each trim section through a pull-downresistor to the source terminal. Activation fuse 162 is blown.Activation fuses 163 and 164 are connected. Since activation fuse 162 isblown, the device of trim section 152 can conduct current from the drainterminal to the source terminal. Therefore trim sections 151 and 152actively conduct current according to the drain source voltage V_(DS)and as controlled by the gate source voltage V_(GS). The thresholdvoltage of element group 150 is the smallest threshold voltage ofsections 151 and 152.

Referring to FIG. 2, an example procedure 200 for trimming an elementgroup to a specific threshold voltage is as follows. At step 202, atarget threshold voltage is selected. At step 204, the threshold voltageof the composite device is measured using a standard linear Vtmeasurement, or a saturated Vt measurement, or a Vt measurement based onan area-weighted drain current specification, depending upon a specificapplication. The threshold voltage of each element group havingdifferent threshold voltages can be determined using a measurement ofthe threshold voltage of the composite device or using measurements ofindividual test devices typically found in semiconductor manufacturingprocesses. At step 206, based on the measured threshold voltage fromstep 204, a calculation is made of a number of trim sections to removeto achieve the target threshold voltage. At step 208, starting with theright-most isolation fuse in the element group that is still active,isolation fuses for trim sections are blown from right to left until thecalculated number of trim sections are removed. For example, in FIG. 1D,isolation fuses are blown starting with isolation fuse 174 and endingwith isolation fuse 173. Blowing the isolation fuses from right to leftincreases the overall composite threshold voltage of the device to athreshold voltage approaching the target threshold voltage.

At step 210, the trimmed threshold voltage of the composite device ismeasured. At step 212, if the trimmed threshold voltage is still lowerthan the target threshold voltage, then the procedure is repeated,beginning with step 206, until the target threshold voltage is attained.

At step 212, if the trimmed threshold voltage is greater than the targetthreshold voltage or equal to the target threshold within a predefinedtolerance range, the procedure moves to step 218 where each remainingtrim section (each trim section to the left of the last blown isolationfuse) in the element group is permanently enabled by blowing itscorresponding activation fuse. For example, in FIG. 1D, activation fuse162 is blown since isolation fuse 173 is the last blown isolation fuse.

Referring to FIG. 3A, a composite VDMOS device 300 consists of a set ofm device trim sections including device trim sections 332, 334 and 336connected in parallel to each other and to a primary device 301. Thegate electrode of primary device 301 is connected to gate terminal 322,the drain electrode of primary device 301 is connected to drain terminal338 and the source electrode of primary device 301 is connected tosource terminal 340.

Device trim section 332 is connected in parallel to primary device 301through isolation fuse 324. An additional set of (m−3) device trimssections 335 are connected between device trim section 334 and devicetrim section 336. A set of m isolation fuses including isolation fuses324, 326 and 330 are connected in series to gate terminal 322. A voltageV_(DS) is applied between the drain terminal and the source terminal anda voltage V_(GS) is applied between the gate terminal and the sourceterminal.

Trim section 332 includes device 302, with its drain electrode connectedto drain terminal 338 and its source electrode connected to sourceterminal 340. The gate electrode of device 302 is connected to gateterminal 322 through isolation fuse 324. The gate electrode of device302 is further connected to source terminal 340 through pull-downresistor 308 in series with activation fuse 314.

Trim section 334 includes device 304, with its drain electrode connectedto drain terminal 338 and its source electrode connected to sourceterminal 340. The gate electrode of device 304 is connected to gateterminal 322 through isolation fuse 326 and isolation fuse 324. The gateelectrode of device 304 is further connected to source terminal 340through pull-down resistor 310 in series with activation fuse 316.

Trim section 336 includes device 306, with its drain electrode connectedto drain terminal 338 and its source electrode connected to sourceterminal 340. The gate electrode of device 306 is connected to gateterminal 322 through isolation fuse 330, isolation fuse 326, isolationfuse 324 and all intermediate isolation fuses connected in seriesbetween isolation fuse 330 and isolation fuse 326. The gate electrode ofdevice 306 is further connected to source terminal 340 through pull-downresistor 312 in series with activation fuse 318.

There are (m−3) intermediate trim sections between trim section 334 and336 in element group 300 interconnected similarly as trim sections 332,334 and 336 to gate terminal 322, drain terminal 338 and source terminal340.

Referring to FIG. 3B an exemplary device layout for composite device 300has a conducting area A_(total) which is divided between the conductingarea A₀ of primary device 301 and the sum of the conducting areasA_(trim) of the set of device trim sections 332, 334, 335 and 336. Theprimary device, having a conducting area A₀, contributes an areafraction F₀=A₀/A_(total) to the conductance of the composite device. Asingle device trim section, having a conducting area A_(trim),contributes an area fraction F_(trim)=A_(trim)/A_(total) to theconductance of the composite device and to the correspondingon-resistance of the composite device.

In an embodiment of composite device 300, with no electrically isolatedtrim sections, composite device 300 has an on-resistance that is lessthan a desired on-resistance. In another embodiment of composite device300 with no electrically isolated trim sections, composite device 300has a current-carrying capability that is greater than a desiredcurrent-carrying capability. In an additional embodiment, theon-resistance of composite device 300 is selectable to within a desiredtolerance range by electrically isolating a subset of trim sections. Inanother embodiment, the current-carrying capability of composite device300 is selectable to within a desired tolerance range by electricallyisolating a subset of trim sections.

Referring to FIG. 4, an example procedure 400 for trimming compositedevice 300 to a target on-resistance is described as follows. At step402, a target on-resistance R_(target) is selected where R_(target) isgreater than the on-resistance of the untrimmed composite VDMOS device.At step 404, the on-resistance of the untrimmed composite VDMOS deviceis measured. In a preferred embodiment, the measurement of on-resistanceis performed in the linear region of the composite VDMOS device. Exampleconditions for measuring on-resistance are to measure I_(d) (draincurrent) when V_(gs) is set to 10V and when V_(ds) is set to 0.1V; thenon-resistance is calculated as I_(d)/V_(ds).

At step 406, based on the measured on-resistance from step 404, acalculation is made to determine how many of the trim sections to removeto achieve the target on-resistance. When the measured on-resistance isless than the target on-resistance, there is a positive percentagedifference between the target on-resistance and the measured compositeon-resistance given by ΔR=(R_(target)−R_(meas))/R_(meas). Then, thenumber of trim sections to remove is given by N_(remove)=ΔR/F_(trim).

For example, consider a composite VDMOS device as in FIG. 3B with aprimary device and n=20 (twenty) device trim sections where the primarydevice has one-half (50%) of the composite device's conducting area,A_(total), and each device trim section has an area A_(trim) of onefortieth of the composite device's conducting area. ThenF_(trim)=A_(trim)/A_(total) is 2.5%. If the target on-resistance is 5%greater than the measured on-resistance of the untrimmed compositedevice, then dividing ΔR=5% by F_(trim)=2.5% indicates that two of thedevice sections should be trimmed to approach the target. If the targeton-resistance is 7% greater than the measured on-resistance, thendividing 7% by 2.5% indicates that approximately three of the devicesections should be trimmed to approach the target on-resistance. Thisexample implementation is not intended to be limiting. Otherimplementations can involve more or fewer device trim sections and/ordevice trim sections having unequal conducting areas by design.

The procedure 400 continues at step 408, where, starting with theright-most isolation fuse that is still active, isolation fuses areblown until the calculated number of trim sections is removed. Blowingthe isolation fuses from right to left increases the overallon-resistance of the device. For example, in FIG. 3A, isolation fusesare blown starting with isolation fuse 330 and ending with isolationfuse 324. At step 410, the trimmed on-resistance of the composite deviceis measured.

At step 412, the trimmed on-resistance is compared to the targeton-resistance and if the trimmed on-resistance is still lower than thetarget on-resistance and not within a predefined tolerance of the targeton-resistance, then the procedure is repeated, beginning with step 406,until the target on-resistance is attained.

At step 412, if the trimmed on-resistance is within a predefinedtolerance range of the target on-resistance, step 418 is performed,where each remaining trim section (each trim section to the left of thelast blown isolation fuse) is permanently enabled by blowing itscorresponding activation fuse. For example, in FIG. 3A, activation fuse314 is blown when isolation fuse 326 is blown.

An analogous procedure to procedure 400 is followed for trimming thecurrent-carrying capability (conductance) of a composite device to meeta target current-carrying capability where the untrimmed compositecurrent-carrying capability is greater than a trimmed current-carryingcapability. This same procedure may be used to match the on-resistanceor current-carrying capability of two or more IGBTs, or two or morevertical diodes, on the same or on separate die.

Referring to FIG. 5A, a third embodiment of a VDMOS device architectureis described where a trimmable VDMOS device element 500 includes a VDMOSdevice 512 connected in series with a trimmable gate resistor 505 to agate terminal 514. VDMOS device 512 has a source electrode 518, a drainelectrode 516 and a gate electrode 510 where the gate electrode has anintrinsic resistance 506. Gate electrode 510 is connected to trimmablegate resistor 505 which includes a set of r gate resistors 502 connectedin parallel through a set of gate fuses 504. The switching time oftrimmable VDMOS device element 500 is selectable by blowing one or moreof the set of gate fuses 504. The number of parallel gate resistors rmay be any number greater than one based on device size limitations andtrim precision requirements. In a related embodiment, each parallel gateresistor in the set of r gate resistors has a different resistance andin another related embodiment, each parallel gate resistor has the sameresistance.

Referring to FIG. 5B, an example configuration of the trimmable gateresistor is shown. Trimmable gate resistor 525 is connected between gateterminal 534 and gate electrode 530. Trimmable gate resistor 525includes trimmable resistors 540-544 connected in parallel through gatefuses 551-555. Gate fuse 551 and gate fuse 552 are blown. Gate fuses553-555 are connected. The resistance of the trimmable gate resistor asconfigured in FIG. 5B is the resistance of the parallel resistivenetwork of the resistors 542-544 which is greater than the resistance ofthe original parallel resistive network of resistors 540-544.

Referring to FIG. 6, an example procedure 600 for trimming VDMOS deviceelement 500 to a specific switching time is as follows. At step 602, atarget switching time is selected. At step 604, the switching time ofthe untrimmed device is measured using techniques well-known in theindustry. At step 606, the measured switching time is compared with thetarget switching time and a prediction is made of a number of parallelgate fuses that must be blown to achieve the target switching time. Atstep 608, the number of parallel gate fuses is blown, removing theircorresponding parallel gate resistors from trimmable gate resistor 505.At step 610, the switching time T_(trim) of the trimmed VDMOS deviceelement is measured. At step 612, the switching time T_(trim) of thetrimmed VDMOS device element is compared to the target switching time,T_(target). If T_(trim) is greater than or equal to T_(target) within apredefined tolerance, then the procedure ends. If the T_(trim) is stillless than T_(target), then the procedure repeats at step 606.

At step 606 the number of parallel gate fuses to blow is determined asfollows. Switching time is proportional to gate resistance; therefore,an increase in gate resistance by a certain percentage increases theswitching time by the same percentage. For a number of r of parallelresistors, with each parallel gate resistor having the same resistance,removing one parallel resistor from the trimmable resistor device raisesthe resistance of the trimmable resistor device by (1/r) percent. Whenthe target switching time is greater than the measured switching time,there is a positive percentage difference between the target switchingtime and the measured switching time given byΔT=(T_(target)−T_(meas))/T_(meas). Then, the number of parallel gateresistors to remove from the trimmable resistor device, and thecorresponding number of gate fuses to blow, is given by N_(remove)=rΔT.

For example, consider the configuration shown in FIG. 5B with r=5 (five)trimmable gate resistors. In this example, each of the five trimmableresistors has an identical resistance value, so trimming off eachresistor increases the original composite gate resistance by 20%(one-fifth). If the target switching time value is ΔT=20% higher thanthe initially measured switching time value, then rΔT=1, indicating thatone of the trimmable resistors should be trimmed to cause the switchingtime to approach the target switching time. If the target switching timevalue is 65% higher than the initially measured gate resistance value,then rΔT=(5)(0.65), indicating that approximately three of the trimmablegate resistors should be trimmed to approach the target. In FIG. 5B, twotrimmable gate resistors are removed, resulting in a target switchingtime 40% higher than a gate resistance with all of the trimmable gatefuses connected. This is just an example of implementation. Similarimplementations could include more or fewer trimmable gate resistorsand/or gate resistors having unequal resistance values by design.

FIG. 7 illustrates a fourth embodiment for a VDMOS device architecture.Composite device 700 includes a set of m trimmable composite devices 706connected to internal gate terminal 703. Internal gate terminal 703 isconnected to gate terminal 701 through trimmable gate resistor 702.Trimmable gate resistor 702 includes a set of r gate resistors 704connected in parallel through a set of r gate resistor fuses 705. Thenumber r of parallel elements in trimmable gate resistor 702 may be anynumber greater than one, based on device size limitations and trimprecision requirements.

The set of m trimmable composite devices 706 includes trimmablecomposite device 710 through trimmable composite device 740. Trimmablecomposite device 710 consists of n₁ interconnected device trim sectionsconnected to a primary device 723. The n₁ interconnected device trimsections includes trim sections 711-713. The gate electrode of primarydevice 723 is connected to internal gate terminal 703. A set of n₁isolation fuses including isolation fuses 727-729 is connected in seriesto internal gate terminal 703. The drain electrode of primary device 723is connected to drain terminal 724. The source electrode of primarydevice 723 is connected to source terminal 726. Drain-source voltageV_(DS) is applied between source terminal 726 and drain terminal 724.Gate-source voltage V_(GS) is applied between source terminal 726 andgate terminal 703.

Trim section 711 includes a VDMOS device 714, with its drain electrodeconnected to drain terminal 724 and its source electrode connected tosource terminal 726. The gate electrode of VDMOS device 714 is connectedto internal gate terminal 703 through isolation fuse 727. The gateelectrode of VDMOS device 714 is further connected to source terminal726 through pull-down resistor 717 in series with activation fuse 720.

Trim section 712 includes a VDMOS device 715, with its drain electrodeconnected to drain terminal 724 and its source electrode connected tosource terminal 726. The gate electrode of VDMOS device 715 is connectedto internal gate terminal 703 through isolation fuse 728 and isolationfuse 727. The gate electrode of VDMOS device 715 is further connected tosource terminal 726 through pull-down resistor 718 in series withactivation fuse 721.

Trim section 713 includes a VDMOS device 716, with its drain electrodeconnected to drain terminal 724 and its source electrode connected tosource terminal 726. The gate electrode of VDMOS device 716 is connectedto internal gate terminal 703 through isolation fuses 727-729 and allintermediate isolation fuses connecting isolation fuses 728 and 729. Thegate electrode of VDMOS device 716 is further connected to sourceterminal 726 through pull-down resistor 719 in series with activationfuse 722.

Trimmable composite device 740 consists of n_(m) interconnected devicetrim sections connected to a primary device 753. The n_(m)interconnected device trim sections includes trim sections 741-743. Thegate electrode of primary device 753 is connected to internal gateterminal 703. A set of n_(m) isolation fuses including isolation fuses757-759 are connected in series to internal gate terminal 703. The drainelectrode of primary device 753 is connected to drain terminal 754. Thesource electrode of primary device 753 is connected to source terminal756. Drain-source voltage V_(DS) is applied between source terminal 756and drain terminal 754. Gate-source voltage V_(GS) is applied betweensource terminal 756 and gate terminal 703.

Trim section 741 includes a VDMOS device 744, with its drain electrodeconnected to drain terminal 754 and its source electrode connected tosource terminal 756. The gate electrode of VDMOS device 744 is connectedto internal gate terminal 703 through isolation fuse 757. The gateelectrode of VDMOS device 744 is further connected to source terminal756 through pull-down resistor 747 in series with activation fuse 750.

Trim section 742 includes a VDMOS device 745, with its drain electrodeconnected to drain terminal 754 and its source electrode connected tosource terminal 756. The gate electrode of VDMOS device 745 is connectedto internal gate terminal 703 through isolation fuse 758 and isolationfuse 757. The gate electrode of VDMOS device 745 is further connected tosource terminal 756 through pull-down resistor 748 in series withactivation fuse 751.

Trim section 743 includes a VDMOS device 746, with its drain electrodeconnected to drain terminal 754 and its source electrode connected tosource terminal 756. The gate electrode of VDMOS device 746 is connectedto internal gate terminal 703 through isolation fuses 757-759 and allintermediate isolation fuses connecting isolation fuses 758 and 759. Thegate electrode of VDMOS device 746 is further connected to sourceterminal 756 through pull-down resistor 749 in series with activationfuse 752.

The switching time of composite device 700 is configurable by blowingone or more of the set of r gate resistor fuses 705. The thresholdvoltage, on-resistance and conductance of a trimmable composite devicein the set of m trimmable composite devices is configurable alone or incombination by blowing one or more of the set of isolation fuses in thetrimmable composite device.

Referring to FIG. 8, an example procedure 800 for trimming the switchingtime and independently trimming the threshold voltage of compositedevice 700 is as follows. At step 801, a target switching time isselected. At step 802, a target threshold voltage V_(target) isselected. At step 804, the threshold voltage V_(meas), of the compositedevice, is measured. At step 806, V_(meas) is compared to theV_(target). If, at step 806, V_(meas) is greater than or equal toV_(target) within a predefined threshold voltage tolerance, then, atstep 812, the remaining trim sections are activated by blowing theiractivation fuses and the procedure continues at step 824. If, at step806, V_(meas) is less than V_(target), then the procedure continues atstep 808, where a number of remaining trim sections to remove iscalculated. Then, at step 810, the isolation fuses are blown for thenumber of remaining trim sections to remove, starting from the rightmosttrim section proceeding to the left. The procedure repeats at step 804,until V_(meas) is greater than or equal to V_(target) within thepredefined threshold voltage tolerance.

At step 824, switching time, T_(meas), of the trimmed composite deviceis measured. At step 826, the measured switching time T_(meas) iscompared to the target switching time T_(target). If at step 826,T_(meas) is greater than or equal to T_(target) within a predefinedswitching is time tolerance, then the procedure 800 ends. If at step826, T_(meas) is less than T_(target), then, at step 828, a number ofgate resistors to remove is calculated. At step 830, the calculatednumber of gate fuses is blown. The procedure repeats at step 824 untilT_(meas) is greater than or equal to T_(target) within the predefinedswitching time tolerance.

Referring to FIG. 9A, a fifth embodiment of a VDMOS device architectureis illustrated by a trimmable VDMOS device element 900 where a trimmablegate resistor 905 consists of two fuses per gate resistance segment.Trimmable gate resistor 905 can be substituted in any of the embodimentsrequiring a trimmable resistor element.

Trimmable VDMOS device element 900 includes a VDMOS device 912 connectedin series with trimmable gate resistor 905 to a gate terminal 914. VDMOSdevice 912 has a source electrode 918, a drain electrode 916 and aninternal gate electrode 910 where the internal gate electrode has anintrinsic resistance 906. Internal gate electrode 910 is connected totrimmable gate resistor 905 which includes a set of r gate resistors 902connected in parallel through a first set of gate fuses 903 and a secondset of gate fuses 904 where each gate resistor in the set of r gateresistors is connected in series to the gate terminal through a firstgate fuse and further connected in series to the internal gate electrodethrough a second gate fuse. In this configuration, the parasiticcapacitance associated with any resistors disconnected in the trimmablegate resistor 905 is reduced by blowing both connecting fuses to thedisconnected resistor.

The number of parallel gate resistors r may be any number greater thanone based on device size limitations and trim precision requirements. Ina related embodiment, each parallel gate resistor in the set of r gateresistors has a different resistance and in another related embodiment,each parallel gate resistor has the same resistance.

Referring to FIG. 9B, an example configuration of the trimmable gateresistor is shown. Trimmable gate resistor 925 is connected between gateterminal 934 and gate electrode 930. Trimmable gate resistor 925includes trimmable resistor 950 connected to gate terminal 934 throughgate fuse 940 and connected to internal gate electrode 930 through gatefuse 960. Trimmable gate resistor 925 also includes trimmable resistor951 connected to gate terminal 934 through gate fuse 941 and connectedto internal gate electrode 930 through gate fuse 961. Trimmable gateresistor 925 also includes trimmable resistor 952 connected to gate fuse942 and connected to gate fuse 962. Trimmable gate resistor 925 alsoincludes trimmable resistor 953 connected to gate fuse 943 and connectedto gate fuse 963. Trimmable gate resistor 925 also includes trimmableresistor 954 connected to gate fuse 944 and connected to gate fuse 964.

Gate fuses 942-944 and gate fuses 962-964 are blown. Gate fuses 940-941and 960-962 are connected. Gate resistors 952-954 are disconnected fromgate terminal 934 and from gate terminal 930 removing any parasiticcapacitance associated with them. The resistance of the trimmable gateresistor as configured in FIG. 9B is the resistance of the parallelresistive network of the resistors 950-951 which is greater than theresistance of the original parallel resistive network of resistors950-954.

Referring to FIG. 10, in using the trimmable gate resistor of either thethird embodiment of FIG. 5A or the fifth embodiment of FIG. 9A, aprocedure 1000 may be used to trim the gate resistance to a specificgate resistance. For example, gate resistances of two or more VDMOSs orIGBTs can be matched using procedure 1000 on the same or separate die.

At step 1002, a target gate resistance R_(target) is determined. At step1004, the gate resistance R_(gate) between the gate terminal and theinternal gate electrode of an untrimmed device is measured directlyusing probe pads or estimated using measurements of sample devices ortest structures. At step 1006, the measured gate resistance R_(gate) iscompared to the target gate resistance R_(target), and a calculation,based on the difference between R_(gate) and R_(target) and the numberof trimmable resistors in the design, is performed to predict a numberof gate fuses that must be blown to achieve the target gate resistance.At step 1008, the calculated number of gate fuses is blown. At step1010, the gate resistance R_(gate) of the trimmed device is measured. Atstep 1012, the trimmed gate resistance and the target gate resistanceare compared. If, at step 1012, the measured gate resistance is greaterthan or within a desired tolerance of the target gate resistance, theprocedure is stopped. If, at step 1012, the measured gate resistance isless than the target gate resistance and outside of the desiredtolerance, then steps 1006, 1008 and 1010 are repeated until the gateresistance is greater than or within a desired tolerance of the targetgate resistance.

At step 1006, a number of gate fuses to blow is determined. For a numberof r of resistors in a trimmable resistor device, with each resistorhaving the same resistance, removing one resistor from the trimmableresistor device raises the resistance of the trimmable resistor deviceby a fraction 1/r. When the measured resistance is less than the targetresistance, there is a positive percentage difference between the targetresistance and the measured resistance given byΔR_(gate)=(R_(target)−R_(gate))/R_(gate). Then, the number of resistorsto remove, and the number of gate fuses to blow, is given byN_(remove)=rΔR_(gate).

For example, consider a configuration similar to that shown in FIG. 5Awith r=5 (five) trimmable gate resistors and one non-trimmable intrinsicgate resistor. The non-trimmable gate resistor in this example has avalue that is negligible compared to the value of the trimmableresistors. In this example, each of the trimmable resistors has anidentical resistance value, so trimming off each resistor increases theoriginal composite gate resistance by 20% (one-fifth). If the targetgate resistance value is ΔR_(gate)=20% higher than the initiallymeasured gate resistance value, then N=rΔR_(gate)=(5)(0.20), indicatingthat one of the trimmable resistors is to be trimmed to approach thetarget. If the target gate resistance value is 65% higher than theinitially measured gate resistance value, then N=rΔR_(gate)=(5)(0.65),indicating that approximately three of the trimmable gate resistors areto be trimmed to approach the target as shown in the example of FIG. 9B.

For the configuration of FIG. 9A two series connected fuses must beblown to remove a trimmable gate resistor and its related parasiticcapacitance. Similar implementations could include more or fewertrimmable gate resistors and/or gate resistors having unequal resistancevalues by design.

In another embodiment, a specific breakdown voltage of a vertical diodemay be obtained via laser trimming using multiple parallel deviceelements with at least two different breakdown voltages which bracketthe target breakdown voltage. This may also be used to match thebreakdown voltage of two or more vertical diodes on the same or onseparate die. FIGS. 11A-11D illustrate this embodiment. A first elementgroup contains one or more diodes with a first breakdown voltage (V₁),while a second element group contains one or more diodes with a secondbreakdown voltage (V₂), and so forth, with an n^(th) element grouphaving an n^(th) breakdown voltage level (V_(n)). In this embodiment,breakdown voltage V₁ is set to be higher than the second breakdownvoltage V₂, and so forth, with breakdown voltage V_(n-1) set to begreater than breakdown voltage V_(n). The composite breakdown voltage ofthe entire device is set, by the combination and size of the elementshaving breakdown voltage V₁, V₂, etc. through V_(n), to be lower thanthe lowest selectable target breakdown voltage for the device. Trimfuses may be used in element groups to disable a particular diode trimsection within an element group.

The breakdown voltage is commonly defined as the voltage at which theoff-state device begins to electrically break down and pass a specifiedlevel of current. The breakdown voltage is typically measured by rampingthe voltage on the high voltage (V-high) node with respect to the lowvoltage (V-low) node until a specified value of current, typically inthe nanoampere range, is reached.

All of the breakdown voltages are set by standard semiconductor MOSprocessing techniques such as ion implantation. The composite breakdownvoltage of a composite device is set by the lowest breakdown voltage ofthe trim elements remaining after trimming. Since diode breakdown is abreakdown leakage current phenomenon, breakdown voltage can only betrimmed to be a more positive value when removing parallel elements asin this embodiment. Thus the composite breakdown voltage of thetrimmable diode device is purposely set lower than a target range inorder to trim the breakdown voltage positively into the target range.Before any fuses are blown, all of the diode trim elements are enabled(or active). Trim fuses are used to disconnect a diode trim section bydisconnecting it from the high voltage node (V-high).

Referring to FIG. 11A, a diode element 1100 includes one or more diodedevices 1101 connected between a low voltage terminal 1103 and a highvoltage terminal 1102 in a reversed bias configuration. Diode device1101 achieves a device voltage breakdown of V₁. In parallel connectionwith diode element 1100, are one or more diode element groups(illustrated in FIGS. 11B and 11C) connected in parallel with diodeelement 1100, containing diode trim sections, where each diode trimsection comprises one or more diodes connected in series with arespective trim fuse to disable the respective diode.

Referring to FIG. 11B, an element group 1110 consists of one or morediode trim sections, (in this example, m diode trim sections) connectedin parallel between low voltage terminal 1121 and high voltage terminal1120. Diode trim section 1111 includes diode 1114 connected in serieswith a trim fuse 1115 between low voltage terminal 1121 and high voltageterminal 1120 in a reversed bias configuration. Diode trim section 1112includes diode 1116 connected in series with a trim fuse 1117 betweenlow voltage terminal 1121 and high voltage terminal 1120 in a reversedbias configuration. Diode trim section 1113 includes diode 1118connected in series with a trim fuse 1119 between the low voltageterminal 1121 and high voltage terminal 1120 in a reverse biasconfiguration. There are (m−3) additional diode trim sections in elementgroup 1110 connected between low voltage terminal 1121 and high voltageterminal 1120. All of the diode trim sections are connected in parallelbetween low voltage terminal 1121 and high voltage terminal 1120.

All of the diodes in element group 1110 have the same breakdown voltageV₂, where V₂ is lower than V₁. By trimming (or disabling) particulardiodes in the element group, a target amount of current to be passed ata particular breakdown voltage for the overall composite diode devicemay be achieved.

Referring to FIG. 11C, an element group 1130 consists of one or morediode trim sections (in this example, k diode trim sections) connectedin parallel including diode trim sections 1131, 1132 and 1133. Diodetrim section 1131 includes diode 1137 connected in series with a trimfuse 1134 between low voltage terminal 1141 and high voltage terminal1140 in a reversed bias configuration. Diode trim section 1132 includesdiode 1138 connected in series with a trim fuse 1135 also between lowvoltage terminal 1141 and high voltage terminal 1140 in a reversed biasconfiguration. Diode trim section 1133 includes diode 1139 connected inseries with a trim fuse 1136 also between low voltage terminal 1141 andhigh voltage terminal 1140 in a reversed bias configuration. There are(k−3) additional diode trim sections connected between low voltageterminal 1141 and high voltage terminal 1140. All of the diode trimsections are connected in parallel between low voltage terminal 1141 andhigh voltage terminal 1140.

All of the diodes in element group 1130 have a breakdown voltage V_(n),where V_(n) is lower than V₁ and V₂. Again, by trimming (or disabling)particular diodes in the element group, a target amount of current to bepassed at a particular breakdown voltage for the overall composite diodedevice may be achieved. Combining diode element groups, such as 1110 and1130, in parallel with diode element 1100, a target breakdown voltagefor the overall composite diode device may be selected by selectivelydisabling diodes within one or more of the diode element groups.

Referring to FIG. 11D, a configuration of a diode element group isshown. An element group 1150 consists of j diode trim sections connectedin parallel including diode trim sections 1151, 1152, 1153 and 1154.Diode trim section 1151 includes diode 1161 connected in series with atrim fuse 1171 between low voltage terminal 1181 and high voltageterminal 1180 in a reversed bias. Diode trim section 1152 includes diode1162 connected in series with a trim fuse 1172 also between low voltageterminal 1181 and high voltage terminal 1180 in a reversed bias. Diodetrim section 1153 includes diode 1163 connected in series with a trimfuse 1173 also between low voltage terminal 1181 and high voltageterminal 1180 in a reversed bias. Diode trim section 1154 includes diode1164 connected in series with a trim fuse 1174 also between low voltageterminal 1181 and high voltage terminal 1180 in a reversed bias. Thereare (j−4) intermediate diode trim sections 1155 connected between lowvoltage terminal 1181 and high voltage terminal 1180. All of the diodetrim sections are connected in parallel between low voltage terminal1181 and high voltage terminal 1180.

All of the diodes in element group 1150 have the same breakdown voltageV_(n), where V_(n) is lower than breakdown voltage V₁.

In the configuration of FIG. 11D, all trim fuses in element group 1150except trim fuse 1171 and trim fuse 1172 are blown. The compositebreakdown voltage of element group 1150 is determined by the breakdownvoltage of the diode trim sections 1151 and 1152. In a composite diodedevice where device element 1100 is connected in parallel with elementgroup 1150, the composite breakdown voltage of the composite device willbe the combination of the breakdown voltages for the diode(s) in deviceelement 1100 and the breakdown voltages for the enabled (or active)diodes in element group 1150.

Referring to FIG. 12, an example procedure 1200 for trimming a compositediode device containing device element 1100 and element group 1130 to aspecific breakdown voltage is as follows. At step 1202, a targetbreakdown voltage is selected. At step 1204, the breakdown voltage ofthe untrimmed composite diode device is measured between the V-high andV-low terminals. At step 1206, based on the measured breakdown voltage,the target breakdown voltage, and the expected difference in breakdownvoltage between each of the breakdown trim elements, a calculation ismade to determine which diode trim elements in the element group are tobe trimmed. At step 1208, the fuses are then blown for the diode trimelements indicated to be trimmed. Blowing trim fuses corresponding tothe indicated diode trim elements will leave a set of remaining diodetrim elements connected in parallel between the V-high and V-lowterminals. At step 1210, the breakdown voltage VB_(trim) of the trimmedcomposite device is measured.

At step 1212, if the measured breakdown voltage is greater than or equalto the target breakdown voltage within a predefined tolerance, then theprocedure ends. If, at step 1212, the measured breakdown voltageVB_(trim) is still lower than the targeted breakdown voltage VB_(target)and outside the predefined tolerance, then the procedure repeats steps1206, 1208, 1210 and 1212 until the target breakdown voltage isattained.

For example, a composite breakdown voltage target is selected to be495V. If a composite trimmable diode device contains an m=10 diodeelement groups, each containing one trim element, and the expecteddifference in breakdown voltage between the trimmable element groups is1V, then diode trim elements #10, #9, #8, #7, and #6 (corresponding tobreakdown voltages of 490V, 491V, 492V, 493V, & 494V) would be need tobe trimmed in order for the resultant composite breakdown voltage to beset to 495V.

This is just an example of implementation. Similar implementations couldinclude trimmable element groups containing more than one element and/orunequal numbers of elements. The element groups and the elements thereinmight also be designed to have unequal differences in expected breakdownvoltage, including device area-weighted differences.

While the foregoing embodiments illustrate examples where device trimelements are disabled or removed from the composite device operation inorder to alter device parameters, such as to increase the thresholdvoltage, increase the on-resistance, decrease the current-carryingcapability, increase the switching time, or increase the breakdownvoltage for the composite device, the described architecture can bemodified so that trim elements may also be enabled or added to thecomposite device operation, by blowing fuse links to add a trim elementor otherwise enable the operation of a trim element with respect to theoverall composite device, to thereby increase or decrease the desiredparameter for the composite device using the same techniques describedabove.

The embodiments presented in this disclosure are intended to provideimplementable examples of the present invention, but are not intended tolimit the present invention. Other device types besides VDMOS can beused as a base device in a trimmable element group. For example,composite trimmable insulated gate bipolar transistor devices and othervertical MOSFET devices can be constructed using the methods andarchitectures of the disclosure. The disclosed embodiments are also notintended to be limited by the specific trimming devices and methods. Forexample, the trimming can be accomplished with laser fuses blown byapplying laser light from a suitable laser, electrically programmablefuses such as electrically programmable fuses used in conjunction withcharge-trapping non-volatile memory elements, and electrically-blowablefuses and anti-fuses.

The invention claimed is:
 1. A method of making a vertical field effectdevice having a drain terminal, a source terminal and a gate terminal,the method comprising: providing a first field effect device connectedto the drain terminal, the source terminal and the gate terminal;providing a set of second field effect devices, connected to the sourceterminal by a set of parallel activation fuses and connected to the gateterminal by a set of series isolation fuses; measuring a deviceparameter measurement value; comparing the device parameter measurementvalue to a target value; and, if the device parameter measurement valuemeets the target value, then blowing a parallel activation fuse of theset of parallel activation fuses.
 2. The method of claim 1, wherein thestep of blowing further comprises blowing a plurality of parallelactivation fuses of the set of parallel activation fuses.
 3. The methodof claim 1, comprising the further step of: if the device parametermeasurement value does not meet the target value, then blowing a seriesisolation fuse of the set of series of isolation fuses.
 4. The method ofclaim 1, wherein the step of measuring further comprises measuring athreshold voltage.
 5. The method of claim 1, wherein the step ofmeasuring further comprises measuring an on-resistance value.
 6. Themethod of claim 1, wherein the step of providing the set of second fieldeffect devices further comprises the step of: providing a set ofresistors connected to the set of parallel activation fuses.
 7. Themethod of claim 1, wherein the gate terminal is further connected to atrimmable parallel resistor network and further comprising the step of:blowing a parallel resistor fuse of the parallel resistor network.